When someone is lying down, you say *sit **up***.     <br>
When someone is standing in an upright position, you say *sit **down***.

What in the situation when you want to ask a very small kid to sit down to a chair, but the chair is too high for him so he has to *climb **up*** the chair to *sit down* on it?

![picture][1] 

*Sit down* sounds like not matching the context. Would you still use *sit down*? 

What I want to find is if for the native English speaker the phrase *sit down* is stronger than the idea of the logical direction as in *sit up* (which seems more natural to me as the non-native speaker). So if you really *had to* choose and you had no other options, what would you select.

(I believe this is not a duplicate of https://english.stackexchange.com/questions/122019/lying-down-and-then-sit-up-down)


  [1]: https://voiceboks.com/products/wp-content/uploads/2013/10/Going-up-Abiie-group-4.jpg